This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Many colors in feathers, both iridescent (i.e. changing color with angle of reflectance/viewing) and non-iridescent, are created not through pigment deposition but through coherent scattering of light by highly organized nanoscaled tissues. The created color depends on the size and spacing of structural components of the tissue. We hypothesize that this size and spacing is consistent on all three dimensions in non-iridescent tissues, but only in one or two dimensions in iridescent tissues. This difference would explain the constancy of color from non-iridescent, but not iridescent, tissues. We thus propose to use tomography to examine the the three dimensional organization of iridescent and non-iridescent tissues.